The invention concerns a strapping apparatus for strapping goods with a band, the strapping apparatus having a tensioning device which is operatively connected to a tensioning drive and is intended for tensioning the band, a closure device for sealing two ends of a band, and a plurality of rewinding locks for fixing the band in the strapping apparatus.
The invention relates primarily to portable, mobile, i.e. not stationary and permanently installed, strapping apparatuses which are preferably electrically driven and are provided with a mains-independent power supply, such as a storage battery for example. In the case of such apparatuses, there is always the problem that--with a predetermined number of strappings that can be carried out with one storage battery charge--the tensioning force that can be applied as a maximum to each strapping is limited by the relatively low storage battery capacity available. The tensioning force ultimately remaining in a band loop is also reduced by the fact that, during the formation and closing of the band loop, the band is usually guided over a base plate, with which the strapping apparatus rests against the goods. Once the band loop has been closed by friction welding, the strapping apparatus is removed from the goods and the base plate is thereby pulled out of the band loop. Since, as a result, the circumference to be strapped by the already closed band loop is reduced, the tensioning force in the band also subsides.
In order to carry out the welding operation, generally a rotary movement of an electric motor is transformed into a translatory oscillating movement of a welding shoe. The welding shoe in this case presses against one of two layers of (plastic) bands lying one on top of the other, which are heated and welded together as a result.
The invention is therefore based on the object of providing a strapping apparatus with highest possible efficiency, in particular with respect to the utilization of a storage battery charge. In this connection, "efficiency" can be understood to mean the number of strappings with a specific band tension that can be achieved with a specific storage battery capacity. However, it can also be understood to mean the magnitude of the maximum band tension that can be achieved per strapping when carrying out a specific number of strappings--utilizing the full storage battery partial capacity.
The solution according to the invention achieving this object is based on the idea that the electrical energy required by the welding device for welding two layers of the band may also have a considerable influence on the efficiency of a strapping apparatus. Therefore, according to the invention, the respective strapping band is to be brought to the required temperature with a reduced amount of electrical energy. As a result, it is then possible to increase the number of strappings that can be achieved with a storage battery, or to increase the magnitude of the band tension that can be achieved in each strapping. In order to achieve such an improvement, it may be provided in the case of a strapping apparatus mentioned at the beginning that the welding device has a lever, on the one end of which an eccentric which is operatively connected to a motor shaft acts for the purpose of transmitting an eccentric movement, with regard to the motor shaft, to the lever, the other end of which is operatively connected to a welding shoe, the lever being mounted pivotably between its two ends on a pivot spindle, so that the movement of the eccentric results in an oscillating and essentially straight reciprocating movement of the welding shoe. In order that the welding shoe executes an essentially straight movement in spite of the pivoting movement of the lever, there should act (directly or indirectly) on the lever a force, preferably a spring force, which presses the lever during the entire welding operation or sequence of movements in the direction of the base plate and consequently onto the band to be welded. In practice, it has been shown that these measures can contribute to the motor of the welding device having to be supplied with less electrical energy for a friction welding operation than is the case with previously known welding devices. Expressed in another way, the power loss can be reduced in the case of welding devices according to the invention.
In a preferred embodiment of the invention, the motor is arranged on a support, with respect to which the lever can execute only rotary pivoting movements. A solution of a particularly simple structural design is obtained if the lever is mounted directly on the support.
It is preferred here if the eccentric is arranged in a slot-like clearance in the lever, for example a fork, and rests against the said lever at two essentially diametrically opposite points.
In the case of such embodiments of the invention put into practice, it has been found that they permit a particularly quiet welding operation.
A further expedient embodiment of the invention may provide that the support is mounted pivotably about a rotational spindle and the force for pressing the welding shoe onto the band is introduced via the support onto the lever into the welding shoe.
It may also contribute to improving the efficiency if the welding shoe presses the two band layers to be welded onto an abutment support. The abutment support should be serrated and can preferably be arranged on the base plate.
In a further preferred embodiment, a strapping apparatus has at least two rewinding locks, with which the band can be fixed. In this case, the closure device should be arranged between the two rewinding locks. This arrangement has proved successful in particular for applications in which the band is "pulled out" from the closure device by the tensioning device, and not "pushed in", during the tensioning operation. That is to say, it is a structural design of a strapping apparatus in which the tensioning device is arranged behind the closure device in the tensioning direction. It is particularly preferred, however, if a third rewinding lock is present, with which the tensioning wheel can be fixed. In this case, the tensioning wheel should be arrestable, at least against rotational movements in the tensioning direction. With this arrangement it is possible for the band which has been pulled through the closure device during the tensioning operation to be fixed with the already applied band tension for the closing and cutting operation and nevertheless for that section of the band which is subsequently friction-welded and cut to be essentially relieved again of the band tension. This has the advantage that the movement of the welding shoe preferably taking place essentially transversely with respect to the longitudinal extent of the band can be converted better into heat of the band, and that clean cutting edges are produced during cutting of the plastic band. Plastic bands under tension tend to split during cutting.
The invention also concerns a strapping apparatus, mentioned at the beginning, in which control functions for rewinding locks are transmitted from a hand lever to the rewinding locks via a control board. The control board preferably transmits the control functions for all the rewinding locks present. This allows the number of individual parts to be reduced, whereby the weight of the strapping apparatus, intended as a mobile hand-operated apparatus, can be reduced. Since all the control functions are initiated from a central hand lever, operating the strapping apparatus is also made easier as a result.
A structurally particularly simple and space-saving design of a strapping apparatus according to the invention may provide that the control board is connected to the hand lever via a pivot lever. Transmitting means, for example rotational spindles, by which the rewinding locks are transferred from a locking position into an inserting position or vice versa, may be connected to the control board.
Further preferred refinements of the invention emerge from the dependent claims.